In general, mobile devices are computer devices that are small-sized enough to be fit in a pocket and include a display screen having a touch input function or a small-sized keyboard. However, the screen of such a mobile device is often smaller than the sizes of contents provided thereto, and thus a window should be additionally displayed or screen scrolling should be performed. Head-mounted display (HMD) devices should be understood as various image display devices designed for users to view a virtual image while wearing the HMD devices on their heads like eyeglasses. The HMD devices are capable of providing users with not only a simple display function but also with various convenient functions which are combinations of a display function with augmented reality technology, N-screen technology, etc. However, a user of an HMD device should indirectly attempt to control a virtual image displayed on glasses of the HMD device, for example, by making a gesture toward the virtual image, making a voice input, or touching the arms of the eyeglasses without physically touching the virtual image. Thus, the virtual image is difficult to be precisely controlled.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.